Image sensors are widely used in digital still cameras, cellular phones, security cameras, as well as in, medical, automobile, and other applications. Complementary metal-oxide-semiconductor (“CMOS”) technology is used to manufacture lower cost image sensors on silicon substrates. In a large number of image sensors, the image sensor commonly includes several light sensor cells or pixels. A typical individual pixel includes a micro-lens, a filter, a photosensitive element, a floating diffusion region, and one or more transistors for reading out a signal from the photosensitive element. The photosensitive element, floating diffusion region, and gate oxide are disposed on a substrate.
During operation, a CMOS image sensor is exposed to light which is converted into an electrical signal that is read out as a image. However, in conventional CMOS image sensors the electrical signature of an acquired image may often remain embedded in portions of the image sensor, which then appear in subsequently read out electrical signals of subsequently acquired images. The electrical signature of a previously sensed image remaining in the image sensor is often referred to as “ghosting,” “a ghost artifact,” or a “memory effect.” Typically, this memory effect is unwanted and image sensor designers spend considerable effort in trying to eliminate or at least mitigate its presence.